Description of the Prior Art
Quadriplegics, by definition, have impairment of all four limbs, depending on the level and the extent of the spinal cord injury. Even though there may be some residual upper limb or hand function, the chest and abdominal wall muscles below the shoulders are generally paralyzed.
Respiratory impairment is caused by loss of supraspinal control of respiratory muscles below the lesion. Normally ventilation is a complex interaction between the muscles of the chest, abdominal wall, and diaphragm. Spinal cord injury leads to paralysis of inspiratory and expiratory muscles. Loss of abdominal and chest wall expiratory muscles reduce ability to cough and clear secretions.
In the 1950's mortality from respiratory failure in quadriplegia was 100%, decreasing to 11% in the early 1980's. Respiratory problems now comprise a major cause of death in the acute and chronic phases of spinal cord injury (SCI).
A sensitive indicator of respiratory impairment due to neuromuscular disorders is the maximum expiratory pressure (MEP). MEP is greatly decreased due to paralysis of the intercostal and abdominal muscles. Expiration is mostly a passive action, dependent on the recoil of the inflated chest. The impairment of active expiratory pressures results in impaired cough.
The normal MEP ranges from 150-200 cm H.sub.2 O. SCI patients have an MEP reduced to 30% or less. One study showed intrathoracic pressures in SCI patients, as measured by esophageal balloon manometry, to be far below those of normal subjects during coughing.
In pulmonary management of quadripleqia, secretion control is vital to prevent ateleotasis and pneumonia. Fiber optic bronchoscopy and endotracheal suction may be used to prevent such problems. An oscillating kinetic treatment table, such as a Rotorest (trademark of Kinetic Concepts) bed, facilitates postural drainage. However, suction and the use of an artificial airway such as a tracheostomy have the potential for damage to the bronchi due to irritation and trauma that can lead to infection. Suction may also dangerously lower the alveolar oxygen pressure. Chest physiotherapy with chest percussion by a trained attendant is required for patients lacking the ability to cough.
One prior approach to stimulate coughing is known as quad coughing, or huffing, which is the practice by an attendant of pushing the abdomen forcefully to generate the positive airway pressure needed to expel mucus. It has been shown that good quad (quadriplegic) cough results are obtained with full chest insufflation and with the patient in a supine position. Coughing attempts can also be improved by bending the patient forward when sitting.
A prior art device known as the "Cof-Flator" (trademark of Shampaine Industries) was used in polio patients to clear respiratory secretions by delivering a positive pressure air volume followed by a negative pressure. This method required an attendant trained in the use of the "Cof-Flator" device. However the use of this device has the potential for damage to the airways due to excessive suction.
It has also been observed that the loss of nerve supply of the gut and bladder reduces the ability to control voiding of the bowel and bladder and therefore requires an attendant to compress the abdomen of a patient manually. By stimulating the paralyzed abdominal wall to contract, an improved ability to control voiding of the bowel and bladder may be attained for quadriplegic patients.